# How to find the number of elements in band pass filter in ADS?

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#### harryfunk231

##### Newbie level 3
can any1 tell me how to find the number of elements in the filter?
my frequencies are 2.10ghz-2.0ghz
passband return loss <20 db
rejection =25 db @2400 mhz

#### tony_lth

Re: band pass filter in ADS

Use ADS or other software, and it's easy.

harryfunk231

### harryfunk231

Points: 2

#### harryfunk231

##### Newbie level 3
Re: band pass filter in ADS

i know how to design it and calculate the even and odd resistances im in a fix only how to find the number of elements.

#### drkirkby

##### Full Member level 6
Re: band pass filter in ADS

can any1 tell me how to find the number of elements in the filter?
my frequencies are 2.10ghz-2.0ghz
passband return loss <20 db
rejection =25 db @2400 mhz

Your specifications are odd, for several reasons.

Firstly, I suspect you mean

passband return loss >20 dB

or

passband return loss ≧ 20 dB

since what you stated means an SWR of 1.01:1 (return loss 46 dB) would be unacceptable, whereas a SWR of 3:1 (return loss 6 dB) would be OK. I doubt that is what you mean.

Secondly you have put no upper limit on the passband attenuation. Is 20 dB attenuation in the passband acceptable to you? Perhaps you can tolerate 24 dB attenuation in the passband, though I suspect you can't.

Thirdly you specified a rejection of 25 db @2400 mhz. I suspect you mean MHz, not mhz.

Fourthly you have not specified any rejection on the lower frequency side, so your specification indicates a low pass filter, not a band-pass filter.

Neither have you specified any frequencies over which the rejection must exist. You might want it to reject from DC up to your passband, but perhaps it does not matter what the attenuation is at very low frequncies.

You have not specified any range of rejection on the high side. In practice, you are not going to be able to make a filter that has an attenuation of at least 25 dB from 2400 MHz to light. But perhaps you need 25 dB from 2.4 to 10.0 GHz, or perhaps you don't care about anything above 6 GHz.

You say your frequencies are 2.10ghz-2.0ghz. This should be written as GHz, not ghz, but its normal to put the lower frequency first, then the upper frequency. I suspect you mean 2.0 to 2.1 GHz.

You have not specified any passband ripple. That may or may not be important.

You have not specified any impedance value for this. I assume it will be 50 Ω, but you have not stated it.

You have not specified any power handling capability. Does it have to take 1 MW ?

Before worrying what order the filter is, what type of response it has, you need to get clear in your own head exactly what specifications you are trying to meet
. Otherwise, if you simulate or build this, how on earth are you going to know if it meets the specification or not?

Dave

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#### volker_muehlhaus

##### Guest
Re: band pass filter in ADS

You can meet your requirements with 3rd order Chebyshev

#### harryfunk231

##### Newbie level 3
 Passband frequencies from 2170.0-2000.0 MHz;
 Passband return loss < 20 dB;
 Rejection = 25 dB @2400 MHz.

Fabrication substrate: 3M Cu217 with a relative dielectric constant r = 2.17 and a height of 0.794 mm. The copper metallization thickness is t = 35 µm. The devices interfaces are SMA–3.5 mm. connectors, with a characteristic impedance of 50 .

#### BigBoss

 Passband frequencies from 2170.0-2000.0 MHz;
 Passband return loss < 20 dB;
 Rejection = 25 dB @2400 MHz.

Fabrication substrate: 3M Cu217 with a relative dielectric constant r = 2.17 and a height of 0.794 mm. The copper metallization thickness is t = 35 µm. The devices interfaces are SMA–3.5 mm. connectors, with a characteristic impedance of 50 .

I have quickly designed in AWR.

#### Attachments

• FiltyerSchematic.png
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• FilterLayout.png
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#### tony_lth

BigBoss design is good, but in practicle, the design needs margin. Such as for 2000-2170 MHz, maybe need design from 1950M to 2220MHz for the pass band.

#### drkirkby

##### Full Member level 6
I don't see how anyone can give a design, given there is no sensible specification. Based on the data we are given, this is more like a low pass filter than a band pass filter, as there are no specs on the low frequency side of the passband.

Dave

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#### volker_muehlhaus

##### Guest
Dave, the specs are sensible.

You where misinterpreting some of it. For example, the passband ripple can be specified as S11 or as S21 ripple - both is equally valid. You complained about the lack of insertion loss spec, but that is not a required parameter for design. Insertion loss will be minimized by optimizing return loss.

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